The invention concerns an optical element containing a light source with an active side which lights up when an electric tension is applied via electric contacts provided to this end, whereby said light source is mounted against a translucent wall, such that the light of the above-mentioned active side can be seen through this wall.
According to the present state of the art, optical elements of this type contain what is called a light-emitting diode also called LED chip, which is mounted on a metal housing and which is protected by means of a transparent epoxy layer.
These existing elements are disadvantageous, however, in that it is impossible to obtain a homogenous distribution of the produced light intensity. Both the metal housing and the epoxy layer produce interfering phenomena. Thus, in particular in the case of a spherical epoxy layer, this layer may act as a lens. Further, internal reflections in the housing of the LED and in the epoxy layer result in an uncontrolled diffusion of the light coming from the LED.
Temperature variations in the LED due to a varying ambient temperature or changing electric conditions provoke a variation in the emitted light spectrum, which results in an inaccurate perception of the optical element.
These qualities are particularly disadvantageous when such an optical element is used in optical measuring systems where the position of the LED has to be determined by means of a camera. On the basis of the position of the LED is calculated the position and/or orientation of the structure upon which this LED is fixed.
In these optical measuring systems, the optical centre of the LED is determined to allow for an accurate determination of the position, such as for example the centre of gravity of the distribution of the light intensity of the LED. In order to be able to precisely determine a position, it is important that the optical centre of the LED is independent of the angle of detection at which it is perceived, and that the light intensity is as high as possible.
Usually, at least one camera and preferably three cameras are used in such an optical measuring system. A single LED or optical element is observed at different angles by these cameras. A mathematical processor which works in conjunction with these cameras processes the images which are thus formed by said cameras, and on the basis thereof calculates the position of the LED or the optical element.
Thus, the LED""s used according to the prevailing techniques are disadvantageous in that the optical centre of the LED varies as a function of the angle of detection, whereby said internal reflections reduce the light intensity, as a result of which the measuring distance and accuracy are relatively restricted.
The invention aims to remedy these disadvantages by making use of an optical element in an optical measuring system, whereby the position of its optical centre, for example the centre of gravity of the distribution of intensity, is independent of the angle of detection, and which, moreover, has practically no internal reflections, so that a high light intensity is obtained.
To this aim, the above-mentioned translucent wall is formed of transparent fibers provided next to one another in a parallel manner which extend diagonally in relation to the above-mentioned wall.
Practically, said fibers form a plate and they extend almost perpendicular to the surface thereof.
According to a preferred embodiment of the optical element according to the invention, said transparent fibers are glass fibers.
According to a specific embodiment of the optical element according to the invention, a non-transparent coating is provided on said wall on the side of the above-mentioned light source, whereby a recess is provided in this coating on said active side, opposite to the light source.
According to a special embodiment of the optical element according to the invention, a first part of the above-mentioned electrically conductive contacts consists of an electrically conductive coating which is provided on said wall on the side of the light source.
According to an advantageous embodiment of the optical element according to the invention, a layer of conductive material is provided on the side of said light source, which extends opposite to said active side of the latter, forming a second part of the above-mentioned electric contacts.
The invention also concerns a measuring group which is used in an optical measuring system containing several optical elements according to the invention.
Further, the invention also concerns the use of the optical element according to the invention in an optical measuring system.